Non-linear contacts in Ansys Workbench are a type of contact formulation that can model the behavior of contacting surfaces that may separate, slide, or deform under applied loads. Non-linear contacts are useful for simulating problems that involve large displacements, gaps, friction, or contact stiffness1.
There are different types of non-linear contacts in Ansys Workbench, such as frictionless, rough, frictional, and no separation. Each type has its own advantages and disadvantages depending on the problem you are trying to solve. For example, frictionless contact allows free sliding between surfaces but does not account for any shear stresses. Frictional contact can model shear stresses up to a certain limit before sliding occurs, but it may require more iterations to converge. No separation contact prevents any gap formation between surfaces but may not be realistic for some cases1.
To use non-linear contacts in Ansys Workbench, you need to specify the contact and target regions, the contact formulation, the detection method, the contact stiffness, and other advanced settings. You can also use the general contact option to automatically detect and define contacts between all bodies in the model2.
If you want to learn more about non-linear contacts in Ansys Workbench, you can watch some video tutorials here, here, or here. You can also read some articles here, here, or here.
What is the difference between linear and non-linear contacts?
The difference between linear and non-linear contacts is that linear contacts assume a constant contact area and stiffness between the contacting surfaces, while non-linear contacts allow the contact area and stiffness to change depending on the deformation, separation, sliding, or friction of the surfaces1.
Linear contacts are simpler and faster to solve, but they may not be accurate or realistic for some problems that involve large displacements, gaps, friction, or contact stiffness. Non-linear contacts are more complex and slower to solve, but they can capture the true behavior of the contacting surfaces under various loading conditions1.
Some examples of linear and non-linear contacts are:
- Linear: A tube with a torque applied to the end gets larger and larger in diameter2.
- Non-linear: The tube rotates instead of getting larger2.
- Linear: A resistor with a constant resistance that follows Ohm’s Law3.
- Non-linear: A resistor with a varying resistance that depends on external factors3.
- Linear: A molecule with all atoms connected in a straight line4.
- Non-linear: A molecule with atoms connected in more complex shapes4.
What are some examples of non-linear contacts?
Some examples of non-linear contacts are:
- A rubber boot seal that undergoes large strain, large deformation, and contact with other surfaces1.
- A metal forming process that involves plastic deformation, friction, and contact between the die and the workpiece2.
- A tire analysis that considers the large deformation of the rubber material, the contact between the tire and the road, and the inflation pressure2.
- A medical device analysis that models the interaction between the device and the human tissue, such as a stent, a catheter, or an implant2.
These are some of the problems that require non-linear contact analysis to capture the true behavior of the contacting surfaces under various loading conditions.
Explanation about the detection method and stiffness settings for non-linear contacts
I will try to explain more about the detection method and stiffness settings for non-linear contacts in Ansys Workbench.
The detection method is the way that Ansys Workbench identifies the contact pairs between the contact and target regions. There are five options for the detection method: nodal, nodal-normal-to-target, projection, projection-normal-to-target, and closest-point projection1. Each option has a different algorithm for finding the contact nodes and elements, and may result in different contact areas and forces. The default option is nodal-normal-to-target, which is the fastest and most robust option, but it may not be accurate for some cases where the contact surfaces are curved or have sharp corners1. You can change the detection method to another option if you observe excessive penetration or unrealistic results in your simulation.
The stiffness settings control how stiff or flexible the contact interface is in the normal and tangential directions. The stiffness factor is a multiplier that adjusts the contact stiffness based on the material properties of the contact and target regions. The default value is 1.0, which means that the contact stiffness is equal to the harmonic average of the Young’s modulus of the contact and target regions2. You can increase or decrease the stiffness factor to make the contact interface stiffer or softer, respectively. This may affect the convergence and accuracy of your simulation. For example, a higher stiffness factor may reduce the penetration but increase the numerical instability, while a lower stiffness factor may increase the penetration but improve the convergence2.
The stiffness settings also include an option to update the normal stiffness in each iteration. This option allows Ansys Workbench to automatically adjust the contact stiffness based on the current deformation and penetration of the contact interface. This option is recommended for most non-linear contact problems, as it can improve the accuracy and convergence of your simulation3. However, it may also increase the computational cost and time of your simulation.
I hope this explanation helps you understand more about the detection method and stiffness settings for non-linear contacts in Ansys Workbench.
What is the difference between frictional and no separation contact?
Frictional and no separation contact are two types of non-linear contact formulations in Ansys Workbench. They differ in how they model the tangential behavior of the contacting surfaces1.
Frictional contact allows the surfaces to slide relative to each other if the shear stress exceeds a certain limit, which is determined by the coefficient of friction. The coefficient of friction can be constant or variable, depending on the material properties and the contact pressure. Frictional contact can capture the effects of friction on the deformation, stress, and heat generation of the contacting surfaces2.
No separation contact prevents any sliding or separation between the surfaces in both normal and tangential directions. The surfaces are effectively glued together, but they can still deform under applied loads. No separation contact can be used to model problems where the surfaces are bonded or welded, or where the sliding is negligible compared to the deformation3.
Frictional and no separation contact have different advantages and disadvantages depending on the problem you are trying to solve. Frictional contact can be more realistic and accurate for some cases, but it may also require more iterations and computational time to converge. No separation contact can be simpler and faster to solve, but it may not be applicable or realistic for some cases1.
What is the difference between frictional and frictionless contact?
The difference between frictional and frictionless contact is that frictional contact considers the effect of friction forces between the contacting surfaces, while frictionless contact ignores them. Friction forces can resist the relative sliding of the surfaces and generate heat and wear. Frictionless contact assumes that the surfaces can slide freely without any resistance or energy loss.
Frictional and frictionless contact are two types of non-linear contact formulations in Ansys Workbench. They are used to model problems that involve large displacements, gaps, or contact stiffness between the contacting surfaces. Frictional and frictionless contact differ in how they calculate the tangential forces and displacements at the contact interface1.
Frictional contact uses a Coulomb friction model to determine the tangential forces and displacements. The tangential force is proportional to the normal force and the coefficient of friction, which can be constant or variable. If the tangential force exceeds a certain limit, the surfaces start to slide relative to each other. The sliding causes heat generation and wear at the contact interface2.
Frictionless contact assumes that the tangential force is zero and the surfaces can slide without any resistance. The tangential displacement is calculated by integrating the relative velocity of the surfaces over time. The sliding does not cause any heat generation or wear at the contact interface3.
Frictional and frictionless contact have different advantages and disadvantages depending on the problem you are trying to solve. Frictional contact can be more realistic and accurate for some cases, but it may also require more iterations and computational time to converge. Frictionless contact can be simpler and faster to solve, but it may not be applicable or realistic for some cases1.
When to use no-separation, frictional and frictionless contact in Ansys Workbench?
The choice of contact type in Ansys Workbench depends on the problem you are trying to solve and the behavior of the contacting surfaces. Here are some general guidelines for when to use no-separation, frictional and frictionless contact:
- No-separation contact: Use this contact type when you want to prevent any gap formation between the surfaces, but allow some sliding in the tangential direction. This contact type is linear and fast to solve, but it may not be realistic for some cases where the surfaces can separate or open slightly. For example, you can use no-separation contact to model problems where the surfaces are bonded or welded, or where the sliding is negligible compared to the deformation1.
- Frictional contact: Use this contact type when you want to model the effect of friction forces between the surfaces, which can resist the relative sliding and generate heat and wear. This contact type is nonlinear and slow to solve, but it can be more accurate and realistic for some cases where the friction is important or significant. For example, you can use frictional contact to model problems where the surfaces have a rough or sticky texture, or where the sliding is large or frequent2.
- Frictionless contact: Use this contact type when you want to ignore the effect of friction forces between the surfaces, which means that the surfaces can slide freely without any resistance or energy loss. This contact type is also nonlinear and slow to solve, but it can be simpler and faster than frictional contact. For example, you can use frictionless contact to model problems where the surfaces have a smooth or slippery texture, or where the friction is negligible or small2.
These are some general guidelines for when to use no-separation, frictional and frictionless contact in Ansys Workbench. However, you may need to experiment with different contact types and settings to find the best fit for your specific problem.
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